We've kept bees active in Montana winters, rearing brood in greenhouses and 
 flight chambers.  In these settings, humidity is an issue - and it is  
reported to be a critical issue in every study that I've seen of how to keep  
bees indoors during the winter for research trials.  Guelph had, may still  
have, and indoor facility.  The Germans spent some years working with  indoor 
bees.
 
Its seems that too dry, no brood.  The tricky thing is not to go too  far 
in the other direction.  In our climate, which tends to be semi-arid,  we 
often have, both indoors and out, low humidity.  But, when I've  worked with 
bees on either coast, we found that bees don't control high humidity  levels 
very well - outdoor hives fitted with humidity probes usually had  interior 
humidity levels that exceeded ambient air levels.
 
Books imply bees regulate humidity much as they do temperature.  Our  RH 
recordings indicate that if they can get to water, they will increase  
humidity levels above ambient, when its very dry; but they don't do a very good  
job of bringing levels down, such as when moisture condenses under the lid, or 
 when they're driving water out of nectar (which I guess should be  
obvious).  So, the lids that I've seen propped up in wetter climates on the  coasts 
makes sense - let the water drain out, encourage air circulation.  
 
In our area, we tend to be too dry.  Jerry
 
 

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